STORMS. 257 



CHAPTER XVI. 



STORMS. 



Typhoons, ^ 559. — Cyclones, 561. — West India Hurricanes, 562. — Eitra-tropical 

 Gales, 563. — The San Francisco's Gale, 564. — These Gales seldom occur at cer- 

 tain Seasons, 565. — Most prevalent Quarter for the Gales beyond the Calm Belt of 

 Capricorn, 566. — Storm and Rain Charts, 567 257 



558. Plate V. is constructed from data furnished by the Pilot 

 Charts, as far as they go, that are in process of construction at the 

 National Observatory. For the Pilot Charts, the whole ocean is 

 divided off into districts of five degrees square, i. e., five degrees of 

 latitude by five degrees of longitude, as already explained on page 

 23. Now, in getting out from the log-books materials for show- 

 ing, in every district of the ocean, and for every month, how nav- 

 igators have found the winds to blow, it has been assumed that, 

 in whatever part of one of these districts a navigator may be when 

 he records the direction of the wind in his log, from that direc- 

 tion the wind was blowing at that time all over that district ; and 

 this is the only assumption that is permitted in the whole course 

 of investis^ation. 



Now if the navigator will draw, or imagine to be drawn in any 

 such district, twelve vertical columns for the twelve months, and 

 then sixteen horizontal lines through the same for the sixteen 

 points of the compass, i. e., for N., N.N.E., N.E., E.N.E., and so 

 on, omitting the by-^omXs, he will have before him a picture of 

 the "Investigating Chart," out of which the "Pilot Charts" are 

 constructed. In this case, the alternate points of the compass 

 only are used ; because, when sailing free, the direction of the 

 wind is seldom given for such points as N. by E., W. % S., &;c. 

 Moreover, any attempt, for the present, at greater nicety, would be 

 over-refinement ; for navigators do not always make allowance 

 for the aberration of the wind ; in other words, they do not allow 

 for the apparent change in the direction of the wind caused by the 

 rate at which the vessel may be moving through the water, and 

 the angle which her course makes with the true direction of the 



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